1. Field of the Invention
The invention relates generally to shaped charges for perforating, particularly shaped charges having reactive liners.
2. Background Art
After a well has been drilled and casing has been cemented in the well, perforations are created to allow communication of fluids between pay zones in the formation and the wellbore. Shaped charge perforating is commonly used, in which shaped charges are mounted in perforating guns that are conveyed into the well on either an electric line (e.g., a wireline) or tubing (e.g. production tubing, drill pipe, or coiled tubing).
FIG. 1 shows that, after a well 11 is drilled, a casing 12 is typically run in the well 11 and cemented to the well 11 in order to maintain well integrity. After the casing 12 has been cemented in the well 11, one or more sections of the casing 12 that are adjacent to a formation zone of interest, otherwise referred to as a “target zone,” may be perforated to allow fluids from the target zone 13 to flow into the well for production to the surface or to allow injection fluids to be applied into the target zone 13. To perforate a casing section, a perforating device, such as a perforating gun 15, may be lowered into the well 11 to a desired depth, such as at a depth corresponding to the target zone 13 in the surrounding formation 16. Next, one or more shaped charges 20 are fired to create holes in the casing 12 and to create perforations into the target zone 13 of the formation 16. Production fluids in the target zone 13 can then flow through the fractures, through the perforation in the casing, and into the wellbore.
A shaped charge for a perforating device typically includes an energy source located within a shaped charge casing and enclosed with a liner. Energy sources typically include explosive materials. Liners may be made of metals, alloys and/or ceramics. The liner is shaped, such that upon detonation of the explosives, the energy that is released converts the liner material into a directional perforating jet that penetrates the well casing and the adjacent formation to create perforation tunnels. The perforation tunnels allow formation fluids to communicate with the wellbore. In some instance, residual liner material can coat the pores in the perforation tunnel walls and can be harmful to the permeability in the perforation tunnels. On the other hand, these liner materials that are converted into the shaped charge jet can offer an opportunity to enhance the performance characteristics of shaped charges.
In recent years, shaped charges with reactive liners have been developed. The reactive liners are made of reactive materials that can generate additional heat and/or pressure inside the perforation tunnels. Such secondary events can improve the performance characteristics of the shaped charges. For example, a reactive liner composition may include a reactive metal or a reactive metal mixture, such as Al, Ti, Mg, an intermetallic mixture (e.g., Al and Ni), or a thermite mixture (e.g., Al and a metal oxide), that can generate substantial heat inside the newly created perforation tunnels.
The term “thermite” refers to a pyrotechnic composition that comprises a metal powder and a metal oxide. Thermite mixtures can undergo exothermic oxidation-reduction reactions, known as thermite reactions. Most thermite reactions are not explosive in nature, but are characterized by a large energy release in the form of extremely high heat. Aluminum (Al) is among the most common powders used in thermite compositions. Examples of Al-containing thermite compositions include Al/Fe2O3, Al/Fe3O4, and Al/CuO, which are at present incorporated into shaped charge liners.
Thermite reactions generally are more energetic than intermetallic reactions owing to the amount of energy released by the Al oxidation reaction. A major disadvantage related to the incorporation of thermite-type mixtures into shaped charge liners, however, is that the only available method involves the separate addition of each component into the powder mixture used to generate the liners. For example, Al powder and Fe2O3 powder must separately be added into the liner powder mixture. After detonation of the shaped charges, the Al powder and Fe2O3 powder in the penetration jets then need to find each other before the thermite reactions can take place. Thus, the reaction rate may be hindered by the Al and Fe2O3 particles having to “find” each other in order to react, and it is likely that some Al and Fe2O3 remain un-reacted.
An intermetallic composition consists of two or more metallic elements. Some intermetallic compositions can undergo exothermic reactions upon activation. Such exothermic intermetallic reactions may be used for perforating applications. For example, WO 2005/035939, entitled “Improvements in and Relating To Oil Well Perforators,” by Leslie Bates and Brian Bourne, discloses uses of intermetallic reaction systems in shaped charge liners. Specifically, WO 2005/035939 discloses the use of Al/Ni and Al/Pd intermetallic compositions in shaped charge liners to enhance performance.
In addition to uses with a metal oxide, as in a thermite mixture, aluminum can also react with various reagents to produce heat. For example, U.S. Pat. No. 7,393,423 B2, entitled “Use of Aluminum in Perforating and Stimulating a Subterranean Formation and other Engineering Applications,” issued to Liquing Liu in 2008, discloses the use of Al in liners, based on various oxidation reactions.
U.S. Patent Application Publication No. 2009/0078144 A1, entitled “Liner for Shaped Charges,” by Lawrence Behrmann and Wenbo Yang, discloses the use of a variety of energetic metals, including Ti, Mg, and Al, in liners. The Astro Silver™ charges from Schlumberger Technologies (Houston, Tex.) also contain Ti as an energetic material in the liner. These types of shaped charges depend on the reactive elements in the liners to interact with either the explosive decomposition products or materials external to the perforating gun, such as water or the reservoir rock/fluids.
These reactive liners all provide enhancements to shaped charge perforation characteristics. There remains, however, a need to improve upon shaped charge technology and achieve further improvements in shaped charge performance characteristics.